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July 6, 2011

Marijuana-like Chemicals Promote Overeating

by Sam Savage

A new study may shed light on why some people have such a hard time eating only a few potato chips or a single fry.

Researchers at University of California-Irvine found that fats in these foods make them nearly irresistible, and trigger a surprising biological mechanism that likely drives our nearly insatiable appetite for more.

The apparent culprits are natural, marijuana-like chemicals in the body known as endocannabinoids.

In their study, researchers Daniele Piomelli, Nicholas DiPatrizio and colleagues discovered that when rats tasted something fatty, cells in their upper gut started producing endocannabinoids.

The process begins on the tongue, where fats in food generate a signal that travels first to the brain and then through a nerve bundle called the vagus to the intestines.

There, the signal stimulates the production of endocannabinoids, which initiates a surge in cell signaling that prompts the wanton intake of fatty foods, likely by initiating the release of digestive chemicals linked to hunger and satiety that compel us to eat more, Piomelli said.

"This is the first demonstration that endocannabinoid signaling in the gut plays an important role in regulating fat intake," said Piomelli, Director of the UCI School of Medicine's Center for Drug Discovery & Development.

Sugars and proteins did not have this effect, he added.

From an evolutionary standpoint, there's a compelling need for animals to consume fats, which are scarce in nature but vital for proper cell functioning. However, in contemporary human society, fats are readily available, and the innate drive to eat fatty foods leads to obesity, diabetes and cancer, Piomelli said.

The findings suggest it might be possible to curb this tendency by obstructing endocannabinoid activity "“ for example, by using drugs that "clog" cannabinoid receptors.

Since these drugs wouldn't need to enter the brain, they shouldn't cause the central side effects "“ anxiety and depression "“ seen when endocannabinoid signaling is blocked in the brain, Piomelli noted.

The study appears this week in the online edition of Proceedings of the National Academy of Sciences.